Outlines of Comparative Anatomy

the pursuit of this interesting and important study, which has been too mllC neglected in this country?one reason, probably, why physiology, as taug1'1' in many of our schools, remains disfigured by many crude theories and spe' culations, which have long since disappeared on the Continent; tested, a_3 they have been there, by the rigid laws deduced from the successful pursu1' of comparative anatomy, embryogeny or organogenesy, and teratology* ?{ the science of monstrosities. The co-ordinate pursuit of these department of science has given birth to the doctrine of morphology, or the unity of ?f' g-anic elements, which, under the various forms which they assume in d''' ferent classes and genera of animals, is the very foundation of the Frenc.

scarcely more than the records of a number of facts, apparently capable of n? generalization, and shewn to follow no general and uniform laws.
It is to the constant reference to such g-eneral laws that the present work ?Wes its superiority, which cannot fail to render the study of comparative anatomy not only more attractive, and therefore more general, but also useful; calling into exercise, as it will do, the reasoning' powers of the ^md, where hitherto too often the memory only was exercised.
. doubtless, many of our readers possess the course of lectures on this sublet, which appeared last year in the Lancet, and hence may think it unnecessary to possess themselves of the " Cfutlines;" to beginners however Jn the science, we would say, study the " Outlines" first, and, having ob-'ned the elements of the science from this work, you will be able to avail . ?Urselves with much greater benefit of the more extensive view of the sublet presented to your view in the admirable and elaborate course of lecres to which we have alluded. tn the first part of the work, our author, commencing-with the organs of Jation, treats of those of support, of attachment, and of motion; or, in her words, of the osseous, the ligamentous, and the muscular systems; le latter of these subjects, however, is not proceeded far with in this * rt> The plan which our author adopts, is that of commencing with the 0' lowest forms of animal organization, and exhibiting to his readers the aces which are there met with of the systems under review; he then suc-0 Ssiyely takes up the different classes in the ascending scale, and shews not 1 y the gradual additions made to the several organs, in passing-from the difi ^r^ect to the more perfect and finished forms, but also the various mo-haK-atl?ns which the organs undergo, in order to suit them to the peculiar r "S and functions of different animals. Finally, the organs pass under in l6W aS they exist in the most perfect of all animal forms?in man himself, . whom indeed each organ is not seen to attain specifically its most perfect e?opment?a circumstance which would be in the highest degree incon-?Us, and present to our view a monstrous form far stranger than any of bajSe which Nature occasionally exhibits to us ; but in whom that harmonious ancement of the organs, that perfect equipoise, is met with, in which we Sav?eiVe ^ie most Perfect general development of all the organs ; that is to perJ-Gach organ, or rather perhaps each class of organs, assumes the most in *?rm ^iat's compatible with a corresponding degree of development \y8 ot'ler organs. 0Ur 0 proceed to give our readers some idea of the manner in which an(pUth?r handles his subject, and at the same time to introduce a curious tre .lnt;firesting subject to their notice. The fifth section of the first chapter 'ntr Si?^ l'le organs oY support in the vertebrated classes-, in which our author Uces the skeleton to the view of his readers in the following words :? r< Tl c?hun m?st constant and first-formed part of the skeleton is the vertebral Sever ^hich 's composed of moveable vertebrae, each of which consists of and i ^|einents that are found most isolated and distinct in the lowest classes, stant en?bryo state of the highest. The elements which appear most Con-or Qy distinct in the composition of a vertebra are the round central body, Which 0~VertQb'al element, the two superior laminae or peri-verielral elements proces encomPass the spinal chords, the two portions of the superior spinous \r S'P?r, the cpi-vertcbral elements, the two inferior laminae, or para-vertebral *0-XLVl. [Oct. 1 elements, which form a cavity for the blood-vessels, and the two portions of the inferior spinous process, or the cata-vertebral elements. The cyclo-vertebral elements are tubular in the articulated classes of animals where they envelope the whole trunk as hollow segments, they are nearly solid to their centre, and present two concave surfaces in fishes; they are convexo-concave in reptile3, and have flat surfaces in mammalia. They are the most constant and typical parts of the vertebral column. The other vertebral elements vary their forms and positions chiefly according to the dimensions of the organs they embrace, and the extent of surface required for muscular attachment; consequently they vary much in different parts of tly; same column, and in the skeletons of different classes. In the caudal paStion of the skeleton of an osseous fish they are designed to give great extension for the attachment of the powerful lateral muscles which move the tail. The body of the vertebra, or cyclo-vertebral element, supports the two superior laminae or peii-vertebral elements, which early unite above to form the small foramen for the spinal cord; and beyond their termination we observe the interspinous bone and the ray of the external which are the two epi-vertebral elements placed in a vertical line. The analogous elements are seen on the lower part of the vertebra, where the two in* ferior laminae or para-vertebral elements form a large foramen for the lodgment of the great continuation of the aorta above, and the vena cava below. The inferior interspinous bone, and the ray of the external fin, are the two catavertebral elements placed in a vertical line, like the epi-vertebrals above. These vertebral elements often assume, in the region of the abdomen in fishes, another position ; thus the superior elements remain as before indicated, but the inferior laminae or para-vertebrals are stretched out in a horizontal direction, and have the two cata-vertebrals extended from their ends in form of a pair of ribs to encompass the organs of this part of the trunk. The vertebral elements situate above the body of the bone expand in the region of the head in the same manner as we here see those below the cyclo-vertebral element in the region of the abdomen ; and this they do in order to encompass the soft parts contained the cavity of the skull and in the face. The epi and peri-vertebrals are most expanded in the skull and the sacrum, and the para and cata-vertebrals, where they embrace the viscera of the trunk." 59.
The above views with respect to the vertebra are adopted by our author from M. Geoffroy de St. Hilaire, who has published an interestingpaper on the subject in the Mdmoires du Museum.* They form a favourite doctrii10 of the transcendental school, and notwithstanding1 the ridicule which ha9 been attempted to be cast upon it in this country, it may be regarded as o,ie of the best established of those doctrines. Although it was G. H. Hila'1"0 who gave the definite and philosophical view to the theory, with which ^ find it regarded in the pages of our author, yet the doctrine of the sku'1 consisting of a series of vertebral pieces highly expanded and developed was first somewhat incidentally glanced at by J. P. Frank, in the year 179^? in his Delectus Opusculorum Medicorum.

1835]
Outlines of Comparative Anatomy. been advocated with various modifications, by Dumeril, Spix, Blainville, ^arus, Meckel, Cuvier, and Burdacb, with many others. Amongst the first the supporters of this doctrine, we find the Shakespeare of Germany? "Ojithe,* who seems to have had a great predilection for the study of ana-??"ies, and who may be regarded as the very father of vegetable morpho-?87, by which every part of the flower and the fruit is shewn to consist Merely of a modification of the leaf. These various authors, however, whilst agreeing in the general doctrine the skull consisting of a series of vertebral pieces, are not unanimous as to ^ ? number of such pieces entering into its composition. Oken, Dumeril, kPlx> Carus, Cuvier, and Meckel, all unite in assigning three as the number 0 lhe cranial vertebrae, whilst Bojanus regards them as four; Hilaire, how-^Ver? who, as we have seen, has investigated the subject more closely, per-aPs> than any other anatomist, concludes that the skull is composed of ^even vertebral pieces. Hence we find our author, who appears closely 0 follow the last distinguished comparative anatomist in Jiis viexvs on thi$ *u"ject, observes that? ' The number of distinct osseous pieces in the composition of the skull is j^test in fishes, and they correspond nearly with the theory of this part of , ? skeleton, being composed of seven vertebra, each consisting, as usual, of a d>'> with four elements above, and four elements below." VG3.
,.^0r ourselves, however, we must confess that we have always been inined rather to follow the first of these views, which certainly accords better .b what we see in the human cranium, in which we can readily trace the q lstence of a series of three vertebral pieces, which are thus indicated by j,Uvier:??" Le crane se subdivise comme en trois ceintures, formees?
?anterieure par les deux frontaux et l'ethmoide ; l'interm^diaire par les p^~ ejaux et le sphenoide ; la posterieure par l'occipital."t ln this view, we cannot see any thing inconsistent with a fair and legitiq ate use of analogical reasoning, supported, as it is, by the facts observed tracing the modifications of the vertebra and of the cranium through the. ^rious classes of vertebrated animals. Some authors, however, have doubtr JatSs Prevented the general acceptation of the doctrine, by the crude specuand fanciful hypotheses with which they have disfigured it. D [this class of authors we should regard, Spix, who, in a large and exr is t S\Ve ^ias treated of this subject. He believes that, in the cranium, Ve 0 found a perfect repetition of the rest of the skeleton, that of the three pieces entering into its composition ; the superior is the " proper Pnalic" vertebral piece?the second is the " thoracico-cephalic," and the nally, so. also, does the external skeleton of the articulated classes consist of a series of zones or segments, giving a corresponding degree of protection to the same important organs. In these classes, however, the tegumentary system and the skeleton are consolidated together, and the muscles are themselves placed within the vertebral pieces, which here present only one common cavity, from the absence, as we think, of the cyclo-vertebral elements, rather than, as stated by our author, from the " tubular" condition of these elements. The dorsal and the ventral surfaces respectively of the segments of the skeleton, in these classes, appear to us to consist of elements corresponding to the peri-and para-vertebral elements in vertebrated animals, by which names they might appropriately be designated. Indeed, from a somewhat extended consideration of the subject, we are led to the conclusion, that the analogy between the articulated and vertebrated classes is much greater than has yet been generally allowed by comparative anatomists and zoologists; and of which, before we conclude this article, we hope to have convinced such of our readers as have familiarized themselves with the study of comparative anatomy. If our limits had allowed, we could with pleasure have taken this opportunity of directing the attention of our readers to other interesting and important subjects, connected with comparative osteology, but we have already exceeded the limits which we had appointed for the notice of the first part.
In the second part of the work, our author resumes the subject of the muscular system, which was only commenced in the first part, and traces it through the several gradations it exhibits, in passing through the higl'er molluscous classes, from the invertebrate to the vertebrate classes?in the latter of which he treats of it successively in fishes, amphibials, reptiles, birds, 'mammalia, and man himself. As a specimen of the manner in which our author treats this part of his subject, we make the following extract. " The muscles of birds are more red and vascular, more irritable and dense* than in the cold-bloodcd vertebrata beneath them, and they possess these properties in'the greatest degree in the rapacious tribes, where the respiration >s greatest, and where all the functions are most energetic. This condition of the muscular system is required in birds, from the lightness of the medium througj1 which they move, and from their quick and long-contiuued movements throug*1 that element. The muscles are more feeble, pale, soft, and palatable in the heavy, slow-moving, phytophagous tribes, where the condition of the bones, and most of the other systems, mark an inferior or reptile state of development-The fleshy parts of the muscles are generally short and thick, especially in th? arms and legs of birds, and their tendons are generally long, slender, dense, &n often ossified, like many cartilaginous parts of the skeleton. The active, heavy* fleshy parts of the muscles being situate, for the most part, on or near the sol1? trunk of the bird, the extreme parts, so important for progression, are lightened by receiving and supporting only the long, narrow tendons; hence the long, slejj' der legs and the lightness of the arms in this class. As birds have nearly all the same general form and movements, there is remarkable uniformity in the muscular system throughout this class." 165.
*835] Outlines of Comparative Anatomy. 381 ^ the fourth chapter, Dr. Grant considers the nervous system ; and, as ,(; comparative anatomy of this system has assumed, of late, a position of ??nsiderable interest, from the definite nature of the additions made to our _ nowledg-e respecting-it, and from the interesting1 reference which the sub--ect has to human physiology, we will endeavour to present our readers with s succinct an account as may be of the subject.
in c^arac^er ^ie nervous system is one of primary importance, n determiningthe rank which animals hold in the scale of development, ^PPears to be generally admitted by comparative anatomists ; certain chacters distinguish this system, in all the grand divisions of the animal gdom. The two first grand divisions, of vertebrate and invertebrate ani-tlIs> have each their peculiar modification of nervous system?thus : The great ccntral portion of the nervous system is perforated by the alia 1 canal, in the invertebrated classes, either in its middle, as in the radiata v mollusca, or at its anterior extremity, as in the articulata; but, in the ,e"rata, the spino-cerebral axis lies wholly above the digestive cavity, by ich it is no where pierced." 180. ch^1G ^iree ?"rand classes or divisions of invertebrate animals have each a racteristic form of the great nervous centre; and, from this circumstance, j.r-Grant has appropriated to each a name expressive of this difference, in c-v l ^ose in general use ; thus, the terms cyclo-neurose, diplo-neurose, ?"?"angliated, and spini-cerebratcd, are respectively applied to the radi-? the articulated, the molluscous, and the vertebrated classes of animals. selv not Perce^ve ^ie necessity for this innovation, nor are the terms themes beyond.the reach of fair criticism ; but we pass on. anjn the lowest animal forms, those which are embraced by the polyg-astric the ^0r^Pherous classes of radiated animals?the infusoria and sponges of as ?^er zoologists, no distinct nervous system has yet been met with; but, rie?ur author supposes, this is most likely owing to the transparency of the the^?US. laments in these minute animals (the polygastrica), which, from ^ activity of their functions, may be well concluded to possess the ruditeb S' at ^east? that form of this system possessed by the higher inver-PartM0^ c^asses* " In the poriphera (our author thinks that), the component eve 1. 0|^ nervous and muscular systems are probably diffused through livj^ Part ^ie so^ cellular tissue of the body, which possesses the same (je , *= Properties in every part, and is almost indefinitely divisible without \0J?y^S its vitality." In the polypiphera?the zoophyta of the older zooalon S> an<^ comprising the corals and madrepores, it is, in the actinia havV ^ar?"e and naked polypus, that a nervous system appears hitherto to m keen discovered. In this animal, " nervous filaments surround the c0ur M ^00t' beneath the stomach, and present minute ganglia in their Cuja^e' from which nerves pass out to the circumference, and to the muster to'ds, which here possess great power of contraction. The same sys-j^r?bably exists in many other closely-allied forms of polypi." lettl two remaining classes of radiate animals?the acalepha, or seaand the echinoderma, of which the asterias, or star-fish, may be ^et as a familiar instance, the nervous system is pretty constantly ?ariL"l *n ^1C ^orm a circular white cord, surrounding the mouth, with la developed upon it at regular intervals, the number of which ganglia MKBICd-CHIRtJRGICAL RisViEVf.
[Oct, 1 corresponds with tliat of the radiatingsegments of the body. Thus the circular, double nervous cord of the beroe pileus, an acalephous animal, is furnished with eight small white ganglia, interposed between the eight longitudinal bands of cilia, which ganglia supply with minute nervous filaments the various parts of the body ; and in the asterias, which* as before stated* belongs to the echinoderma, a similar circular cord around the mouth has five minute ganglia, corresponding-to the five rays of most species of this animal. In the highest forms of radiated animals, as the holothuria and the siponculus, the nervous system is beginning-to approach that form which Constitutes its type in the articulated classes ; thus, in the latter of these hera, two minute longitudinal nervous filaments extend backwards from the oesophageal ring, and are developed Only on one side of the body, like the abdominal nerves of the helminthoid articulata.
We now come to the consideration Ctf the nervous system in the articulated classes* where, from the striking analogy which recent researches have shewn it to have with that of vertebrate animals, and, hence, with that of man himself, the subject is invested with considerable attraction. The molluscous fclasses, indeed, have had a higher rank assigned them in the scale of animal organization than the articulated, in consequence of the superior development of their organs of nutrition?of their digestive, circulatory, and respiratory systems. But surely, in a zoological classification, the functions Of relation, or, in the expressive languag-e of Bichat, " the functions of animal life," ought to have a higher value assigned to them than those of nutrition, which vegetable forms enjoy in common with animals. In the articulated classes, all the organs of relation, the osseous system (if we may So speak Of their skeleton), the muscular.and the nervous systems, and most of the organs of the senses, have all of them become infinitely more closely assimilated to the more perfect forms which they assume in the vertebrated classes, than is the case in any of the mollusca. We know that> by reversing their order, we should be in no better predicament; the high" est class of the mollusca, the cephalopods, would then be separated widely from the fishes, to which they are doubtless very closely united; but we merely draw attention to this circumstance, in order to point out the clos? analogy that the organs of relation, in the articulata, have with those of the vertebrata. In fine, whilst the molluscous classes, with their superior organ3 Of nutrition, evidently have, through their highest class?the cephalopods> ?f the cord, separating-as they approach the under surface of this tube, and, 'iter encircling it, unite in forming a ganglion, generally the largest in the 0('y. These ganglia give off as many pairs of nerves to the muscles and ?ther organs of their bodies, the supra-cesophageal serving as the origin of several pair distributed to the eyes, the antenna;, and other organs of sense motion seated at the cephalic extremity of the bodies of these animals, "e development of these ganglia is in the direct ratio of that of the organs 0 ^hich they are distributed. This is well exemplified in the four classes instituting the helminthoid section of the articulata ; thus, in the entozoa atul the annelida, which, as they possess either very imperfectly-developed ateral appendices for progressive motion, or else none at all, and, as they e(iually deficient in, or imperfectly supplied with, organs of sense at ?,r anterior extremities, so, also, are their supra-ossophageal and abdomilal ganglia in an equally rudimentary condition, and, indeed, frequently not Perceptible. In the rotifera, however, " where there is a complex muscular apparatus at the anterior extremity of the trunk, for the motion of the nuraerous large cilia, and another muscular apparatus for the movements of the r?ng lateral maxillae, the nervous system is most developed in that part of le body." In these animals, whilst the supra-oesophageal, with its acces-S-Sanglia, are generally distinct and large, the abdominal ganglia are equently absent. In the cirrhopods, as " in the anatifa, we perceive a ender white nervous ring, surrounding the oesophagus, and sending out Yla'l filaments to the surrounding parts, but scarcely forming a perceptible Pra-oesophageal ganglion, from the imperfect development of the sensitive u masticating apparatus in these fixed and inverted testaceous, or cnto-0straceous animals. As the long-jointed and ciliated feet, with their thick j Uscular haunches, and supporting the bronchia^ at their base, are deve-?pecl from the sides of the posterior part of the trunk, the ganglia, like the erv?us columns which connect them, are large in that part of the body, ncl correspond in position with the origin of the several pairs of legs." c ^he nervous system of the entomoid classes presents only a more developed anH the same plan structure presented by this system in the worms, Id that of the most elevated insect or crab begins its development with the sim-0S" helminthoid form." 190.
theFr?m the greater development of the nervous system in this section of artieulated classes, comprising the myriapods, the insects, spiders, and staceous animals, it is here that comparative anatomists have most fully ceeded in unravelling its structure, and have thus advanced comparative rology to its present degree of completeness.
. n the myriapods, as, e. g. in the centipede, we do not find much to deus, their nervotis system presenting only a more developed form of that tin 1 helminthoid classes. With the metamorphoses which are In tfr?0ne hy insects, their nervous system does not remain unchanged, res lG*r-*arva state? they generally present thirteen pairs of ganglia, cors l)(?n(hng with the number of the original segments of the body, which Pply nerves the soft tissues of which they are now composed. These from i ^u"n8" the process of development undergone by insects in passingto a larva, through the pupa, to the imago or perfect state, are observed [Oct. 1 ticularly observed in the thoracic portion of the cords and ganglia, which latter afterwards unite together in the situation most suited to send nerves to the yet undeveloped thoracic members. The nature of these changes produced during development, will be understood by our readers on perusing our author's description of the adult condition of the nervous system in the papilio brassicae, as observed and described twenty years ago by Herold. " In the imago or perfect condition of the insect, the loose inter-ganglionic portions of the columns, which were zig-gag in the pupa, have assumed a straight and shorter form?the two last pairs (the 12th and 13th) have coalesced into one ganglion, and advanced from their original position?the cineritious matter has disappeared from two pairs of the abdominal ganglia (7th and 8th) without affecting the original origins of their nerves?four pair of ganglia (the 6th and 5th, and the 4th and 3d) have coalesced at two points of the thorax, to supply nerves to the muscles of the legs and wings?the second and first pairs of ganglia have approached in the head, and diminished the diameter of the oesophageal ring, (which was much greater during its voracious larva state)?the cephalic ganglia have enlarged and extended transversely to form the expanded optic lobes." 196.
Remarkable as are the changes which take place in the form of the nervous system in this, and in other lepidopterous and hymenopterous insects, they are not nearly so extensive as those which obtain in the coleoptera, and which have been observed by Straus Durckheim in the melolontha vulgaris.
of most other parts of the arachnida, it presents an intermediate condition i98 el?Pment betwixt most insects and that of the higher crustacea." In the highest class of articulated animals, the crustacea, the nervous s) steni is variously developed, according-to the more or less perfect development of the animals themselves. It however, for the most part, affects two ^eneral forms?a lengthened one, like that of mvriapods, as in the lobster, j acus,) and a concentrated one, analogous to what exists in coleopterous Sects, as in the crab-tribe, (maia,)?in these latter our author says?
All the symmetrical ganglia of the columns are generally collected into two a Sscs? the one in the head, and the other in the centre of the cephalo-thorax, the motor and sensitive columns are almost confined to a nervous band Und the wide oesophagus. The anterior of these, or the supra-oesophageal ? nghon, is comparatively small in the brachyourous decapods, from the smallof the cephalic appendices which it supplies with nerves. The infra-cesonervous mass is of great size, consisting of the whole chain of ganglia, fav Was originally extended along the body behind the oesophagus, and is ?urably situated between the haunches of the legs under a strong internal ^jleeoils arch, in the centre of the trunk. It sends out numerous branches to th fSUrr.ounding visccra, and to the five pairs of legs which radiate from around slio ? an(l the columns are prolonged backwards, ramifying along the 0rt slender post-abdomen, as a simple nervous chord." 203. having presented our readers with a general view of the anatomy of the neris l/ System 'n the articulated classes, we will now turn their attention to what nown of its minute structure, and endeavour to shew to what part of the vous system in vertebrated animals it is analogous. Very opposite opi-?n this latter head have been held by anatomists and physiologists :? g. s* pichat, Reil, and Ackermann, with some others, have regarded the shonary cord of insects and the other articulata as analogous to the a .at sympathetic of man, to which view of the question, by-the-bye, our refl0l< t'oes not ac*vert. This doctrine, however, seems to be sufficiently Co ?i ky the distribution of the nerves rising immediately from this double bv tv, W^ich*s almost exclusively to organs of sense and motion, as well as Sy existence of what has appeared to many as the rudiments of a distinct the em 0r?"an'c nerves in most of these classes. There is connected with nc .SuPra-oesophageal and lateral ganglia, (which latter, from their cona ?n> seem to have a close analogy to the first cervical ganglia in man,) rUnsr^0Us filament, having two or three minute ganglia on its trunk, which [Oct* 1 The other view with respect to the nature of the central part of the hervous system in these classes, consists in regarding it as the counterpart of the cerebro-spinal system of man, and the other vertebrata, a doctrine* which as our author states, has been long-held by Lyonet, Straus, Dufour, and Chiaje, amongst those who have investigated this part of the animal creation more particularly, and to whose names we may add those of Scarpa.
Blumenbach, Cuvier, Meckel, and Gall. We will endeavour, as concisely as possible, to point out to our readers the characters of this analogy. That in the insects and higher entomoid classes the supra-oesophageal ganglia?* largely developed as they are, and supplying nerves to the organs of sense?
the eyes and antennse, as well as to those of motion?the maxillae, and even, if our memory do not deceive us, containing, according to Straus Durckheim. ventricular cavities within their substance?are closely analogous to the brain of higher animals, must, we think, be readily acknowledged. But does the ganglionary cord, stretched through their bodies, answer as closely to the spinal cord of the vertebrata ? Is its situation the same as that of the medulla spinalis ? Does it possess two distinct nervous tracts giving origin to nerves having sentient and motiferous properties? And, if so, how does its minute anatomy bear upon the still undecided question respecting the existence of a distinct respiratory system of nerves ? To these questions we will endeavour to give satisfactory answers. In the first place, with respect to its situation, it occupies the abdominal and not the dorsal surface of the body, but then, says our author? the other viscera of the trunk present the same inverted position ; the heartforming portion of the sanguiferous system occupies the dorsal surface," s0 that the great nervous columns may be regarded as being "extended far protection along the ventral or under surface of the body." Medico-chirurgical Rkvikvv.
[Oct. 1 which holds an intermediate position between the motor and sensitive column^.
In order to make our account of the nervous system of invertebratcd animals complete, we extract the followingpassages from the fourth section of the fourth chapter, on the nervous system of the cyclo-gangliated, or molluscous classes. " The nervous system is distinctly developed and provided with several ganglionic centres, in all the molluscous classes, from the lowest compound forms of tunicata to the highest of the cephaloj)ods, and notwithstanding the remarkable diversity of form which the animals of this division present, we can trace a certain similarity of character and unity of place in the development of this system, and in its typical forms, throughout all the cyclo-gangliated classes. In the tunicated and conchiferous animals the columns are chiefly disposed beneath the alimentary canal; in the gasteropods and the pteropods they are more equally distributed around the entrance to the stomach; and in the more elevated forms of ceplialopods they at length mount to that supra-cesophageal p?" sition which they preserve in all the vertebrata where they cease to embrace the alimentary canal." 204.